Physics Opportunities in a NuMI Offaxis Experiment

1. Physics Opportunitiesin a NuMI Offaxis Experiment Stanley Wojcicki Stanford University September 16, 2002 London, England

2. Stan Wojcicki, Physics at Off-axis Outline • Introductory Comments • Advantages of an Off-axis Beam • Important Physics Issues • NuMI Capabilities

3. Stan Wojcicki, Physics at Off-axis Introduction

4. Stan Wojcicki, Physics at Off-axis Introductory Comments The current generation of long and medium baseline terrestial n oscillation experiments is designed to: Confirm SuperK results with accelerator n’s (K2K) Demonstrate oscillatory behavior of nm’s (MINOS) Make precise measurement of oscillation parameters (MINOS) 4. Demonstrate explicitly nmnt oscillation mode by detecting nt’s (OPERA, ICARUS) 5. Improve limits on nmne subdominant oscillation mode, or detect it (MINOS, ICARUS) Resolve the LSND puzzle (MiniBooNE) Confirm indications of LMA solution (KamLAND) Many issues in neutrino physics will then still remain unresolved. Next generation experiments will try to address them.

5. Stan Wojcicki, Physics at Off-axis The Physics Goals • Observation of the transition nmne • Measurement of q13 • Determination of mass hierarchy (sign of Dm23) • Search for CP violation in neutrino sector • Measurement of CP violation parameters • Testing CPT with high precision

6. Stan Wojcicki, Physics at Off-axis Offaxis Beam Advantages

7. Stan Wojcicki, Physics at Off-axis The Off-axis Situation • The physics issues to be investigated are clearly delineated • The dominant oscillation parameters are known reasonably well • One wants to maximize flux at the desired energy (near oscillation maximum) • One wants to minimize flux at other energies • One wants to have narrow energy spectrum

8. Stan Wojcicki, Physics at Off-axis Kinematics of p Decay Compare En spectra from10,15, and 20 GeV p’s • Lab energy given by length of vector from origin to contour • Lab angle by angle wrt vertical • Energy of n is relatively independent of p energy • Both higher and lower p energies give n’s of somewhat lower energy • There will be a sharp edge at the high end of the resultant n spectrum • Energy varies linearly with angle • Main energy spread is due to beam divergence EnLAB qLAB

9. Stan Wojcicki, Physics at Off-axis Kinematics Quantitatively

10. Stan Wojcicki, Physics at Off-axis Optimization of off-axis beam • Choose optimum En (from L and Dm232) • This will determine mean Ep and qLAB from the 90o CM decay condition • Tune the optical system (target position, horns) so as to accept maximum p meson flux around the desired mean Ep

11. Stan Wojcicki, Physics at Off-axis Off-axis ‘magic’( D.Beavis at al. BNL Proposal E-889) NuMI beam can produce 1-3 GeV intense beams with well defined energyin a cone around the nominal beam direction

12. Stan Wojcicki, Physics at Off-axis Medium Energy Beam A. Para, M. Szleper, hep- ex/0110032 Neutrino event spectra at putative detectors located at different transverse locations More flux than low energy on-axis (broader spectrum of pions contributing) Neutrinos from K decays

13. Stan Wojcicki, Physics at Off-axis Experimental Challenge

14. Stan Wojcicki, Physics at Off-axis Physics

15. Stan Wojcicki, Physics at Off-axis 2 Mass Hierarchy Possibilities

16. Stan Wojcicki, Physics at Off-axis nm ne transition equation P (nm ne) = P1 + P2 + P3 + P4 A. Cervera et al., Nuclear Physics B 579 (2000) 17 – 55, expansion to second order in

17. Stan Wojcicki, Physics at Off-axis Several Observations • First 2 terms are independent of the CP violating parameter d • The last term changes sign between n and n • If q13 is very small (≤ 1o) the second term (subdominant oscillation) competes with 1st • For small q13, the CP terms are proportional to q13; the first (non-CP term) to q132 • The CP violating terms grow with decreasing En (for a given L) • There is a strong correlation between different parameters • CP violation is observable only if all angles ≠ 0

18. Stan Wojcicki, Physics at Off-axis q13 Issue • The measurement of q13 is made complicated by the fact that oscillation probability is affected by matter effects and possible CP violation • Because of this, there is not a unique mathematical relationship between oscillation probability and q13 • Especially for low values of q13, sensitivity of an experiment to seeing nmnedepends very much on d • Several experiments with different conditions and with both n and n will be necessary to disentangle these effects • The focus of next generation oscillation experiments is to observenmne transition • q13 needs to be sufficiently large if one is to have a chance to investigate CP violation in n sector

19. Stan Wojcicki, Physics at Off-axis Matter Effects • The experiments looking at nm disappearance measure Dm232 • Thus they cannot measuresign of that quantity ie determine mass hierarchy • The sign can be measured by looking at the rate for nmne for both nmand nm. • The rates will be different by virtue of different ne-e- CC interaction in matter, independent of whether CP is violated or not • At L = 750km and oscillation maximum, the size of the effect is given by A = 2√2 GF ne En / Dm232 ~ 0.15

20. Stan Wojcicki, Physics at Off-axis Source of Matter Effects

21. Stan Wojcicki, Physics at Off-axis Scaling Laws (CP and Matter) • Both matter and CP violation effects can be best investigated if the dominant oscillation phase f is maximum, ie f = np/2, n odd (1,3,…) • Thus Ena L / n • For practical reasons (flux, cross section) relevant values of n are 1 and 3 • Matter effects scale as q132En or q132 L/n • CP violation effects scale as q13Dm122 n

22. Stan Wojcicki, Physics at Off-axis Scaling Laws (2) • If q13 is small, eg sin22q13 < 0.02, then CP violation effects obscure matter effects • Hence, performing the experiment at 2nd maximum (n=3) might be a best way of resolving the ambiguity • Good knowledge of Dm232 becomes then critical • Several locations (and energies) are required to determine all the parameters

23. Stan Wojcicki, Physics at Off-axis CP and Matter Effects

24. Stan Wojcicki, Physics at Off-axis NuMI Capabilities

25. Stan Wojcicki, Physics at Off-axis Important Reminder • Oscillation Probability (or sin22qme) is not unambigously related to fundamental parameters, q13 or Ue32 • At low values of sin22q13 (~0.01), the uncertainty could be as much as a factor of 4 due to matter and CP effects • Measurement precision of fundamental parameters can be optimized by a judicious choice of running time between n and n

26. Stan Wojcicki, Physics at Off-axis CP/mass hierarchy/q13ambiguity Neutrinos only, L=712 km, En=1.6 GeV, Dm232 = 2.5

27. Stan Wojcicki, Physics at Off-axis Antineutrinos help greatly Antineutrinos are crucial to understanding: • Mass hierarchy • CP violation • CPT violation High energy experience: antineutrinos are ‘expensive’. Ingredients: s(p+)~3s(p-) (large x) For the same number of POT NuMI ME beam energies: s(p+)~1.15s(p-) (charge conservation!) Neutrino/antineutrino events/proton ~ 3 (no Pauli exclusion)

28. Stan Wojcicki, Physics at Off-axis How antineutrinos can help resolve the CP/mass hierarchy/q13 ambiguity Antineutrino range Neutrino range L=712 km, En=1.6 GeV, Dm232 = 2.5

29. Stan Wojcicki, Physics at Off-axis Optimum Run Strategy • Start the experiment with neutrinos • Run in that mode until either: • A definite signal is seen, or • Potential sensitivity with antineutrinos could be significantly higher (x 2?) than with neutrinos • Switch to antineutrinos and run in that mode until either: • A definite signal is seen • Potential sensitivity improvement from additional running would be better with neutrinos

30. Stan Wojcicki, Physics at Off-axis Sensitivy for Phases I and II (for different run scenarios) We take the Phase II to have 25 times higher POT x Detector mass Neutrino energy and detector distance remain the same

31. Stan Wojcicki, Physics at Off-axis Concluding Remarks • Neutrino Physics appears to be an exciting field for many years to come • Most likely several experiments with different running conditions will be required • Off-axis detectors offer a promising avenue to pursue this physics • NuMI beam is excellently matched to this physics in terms of beam intensity, flexibility, beam energy, and potential source-to-detector distances that could be available • We have great interest in forming a Collaboration that could work on these opportunities